Contra Costa County prosecutors on Thursday filed felony charges against 15 more Diablo Valley College students in the cash-for-grades scheme, expanding what has become one of the nation’s largest criminal cases regarding academic fraud.

The 25-page complaint details 23 counts of computer fraud and conspiracy, the same charges that were filed against the first 34 defendants earlier this year. The new charges come just days after one ringleader, Jeremy Tato, pleaded no contest to eight felony charges and agreed to help prosecutors in the case.

Tato was sentenced to a year in jail, but he is likely to spend 10 months in home confinement instead. Julian Revilleza, another ringleader, had earlier pleaded guilty to several charges and is spending a year in County Jail.

The six-year-long scandal involved student employees in the DVC records office and resulted in hundreds of grade changes. Students paid hundreds of dollars per change, sometimes taking out cash advances on their credit cards to pay for the alterations.

The bulk of the new charges focus on the activities of Liberato Rocky Servo, a former student employee who is accused of training Revilleza to take over his role as ringleader. Servo, a Vallejo resident who could not be reached for comment Thursday, was charged with 19 counts and could spend 15 years in prison.

He was expected to surrender to authorities Monday. Bail was set at $475,000, said prosecutor Dodie Katague.

Servo was fired from the records office in 2004 in an unrelated incident, Katague said, but he is accused of changing a slew of grades before leaving work for the last time. He continued to provide Revilleza with new orders for grade changes, according to the complaint, much as Revilleza later did with Tato after transferring first to San Diego State, then to Cal Poly San Luis Obispo.

Several of the students named in Thursday’s complaint are suspected of transferring to four-year universities using the falsified transcripts. Among the schools named were Cal State East Bay, San Francisco State, UCLA and UC Riverside.

DVC police are expected this week to call authorities at those universities to arrange arrest warrants. Three defendants among the first 34 charged have not been arrested, including Ronald Nixon, who is suspected of starting the scheme in 2000.

Some of the students charged Thursday are accused of changing failing grades to B’s and A’s. In some cases, according to the complaint, the students failed classes because they plagiarized assignments.

Prosecutors also plan to file charges next week against four Los Medanos College students. Both schools are part of the Contra Costa Community College District.

No other charges are expected after next week, Katague said.

“That’s going to be it,” he said, “unless Servo comes to us and says, ‘Here’s a bunch of names you don’t know about.'”

The plot was discovered early in 2006 after a teacher became suspicious about a student who reappeared on a class roster after being dropped. DVC leaders kept the investigation under wraps for a year, saying later that they did not want to alert suspects.

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